Selenium rectifier



Feb 7, 1950 w. E. BLACKBURN 5,

SELENIUM RECTIFIER Filed March 20, 1947 Cadmium- W'n Ga Ilium Cadmium Sulph ide Selenium feel WITNESSES: INVENTOR Wayne E. Blackburn KW V W1 72%W BY Patented Feb. 7, 1950 SELENIUM RECTIFIER Wayne E. Blackburn,Hollywood, Calif., assignor Westinghouse Electric Corporation, EastPittsburgh. Pa., a corporation of Pennsylvania Application March 20,1947, Serial No. 735,883

8 Claims.

My invention relates to selenium rectifiers and. in particular, to acounter-electrode which produces an improved barrier layer. orrectifying interface in such rectifiers. It is based on the discoverythat an improved rectifying ratio atv a surface of selenium, orparticularly a seleniumcadmium sulphide surface, is obtained byemploying a counter-electrode of cadmium, or cadmium, or cadmium-tin, towhich have been made small'additions of gallium, boron. cerium selenlde,columbium oxide or a metal from the alkali or alkaline-earth groups.

One object of my invention is, accordingly. to produce an improvedselenium rectifier.

Another object of my invention is to produce a dry-contact typerectifier having a better rectification layer than rectifiers of theprior art.

Still another object of my invention is to provide a dry-contact ty'perectifier of the type employing selenium surfaced with cadmium sulphidewith a counter-electrode which improves the barrier layer of therectifier.

A yet further object of my invention is to provide an improved type ofcounter-electrode for rectiflers of the selenium type.

Other objects of my invention will become apparent upon reading thefollowing description, taken in connection with the drawing in which:

Figure 1 is a mid-section and Fig. 2 a top view of a rectifier embodyingthe principles ofmy invention.

Referring in detail to Figs. 1 and 2, a rectifier in accordance with myinvention may be produced by employing a backing plate I of steel. whichmay have a central'hole 2 and which has preferably been sand-blasted andnickel-plated. This plate is coated with a layer I of amorphous seleniumby dipping it in a molten bath of selenium and throwing off the excessthereof by centrifugal force. The free surface of the selenium is thencoated by evaporation and condensation with a thin layer 4 of cadmiumsulphide. This procedure may be carried out as described in more detailin my copending application, Serial No. 514,371, filed December 15,1948.

The unit thus produced may then be annealed at a temperature of 185 C.,and the counter-electrode 5 then applied by Bchoop-spraying or othersuitable process known in the art. While I have described the seleniumas coated with cadmium sulphide before the application of thiscounterelectrode, for certain purposes it may be suitable to omit thecoating with cadmium sulphide. Furthermore, it is within the scope of myinvention to apply the counter-electrode before carry- 5 2 ing out theannealing process mentioned above.

The counter-electrode is formed from an alloy or aggregate comprisingsubstantially parts cadmium, 30 parts tin, with the addition of a smallamount, about 1 part of one or more substances from the following group:an alkali or alkaline-earth metal, gallium. boron, cerium selenlde andcolumbium oxide.

Of the addition agents just listed, I have found gallium to beparticularly desirable in cases where the counter-electrode is appliedbefore the heat treatment above mentioned is given, inasmuch as thistreatment does not cause tarnishing oi the alloy containing gallium.

I claim as my invention:

1. A rectifier comprising a barrier layer between selenium surfaced withcadmium sulphide and an alloy containing cadmium, tin and galum.

2. A rectifier comprising a barrier layer between selenium surfaced withcadmium sulphide and an alloy of substantially '10 partscadmium, 30parts tin and up to one part of gallium.

3. A rectifier comprising a barrier layer between selenium and an alloycontaining cadmium, tin and gallium.

4. A rectifier comprising a barrier layer between selenium and an alloyof substantially '70 parts cadmium, 30 parts tin and about one part ofgallium.

5. An electrical circuit element comprising selenium in contactwith analloy of cadmium combined with about 1 of gallium.

6. An electrical circuit element comprising selenium surfaced withcadmium sulphide in contact with an alloy of cadmium combined with about1% of gallium.

I. An electrical circuit element comprising selenium in contact with analloy of cadmium-tin .combined with about 1 of gallium.

8. An electrical circuit element comprising selenium surfaced withcadmium sulphide in contact with an alloy of cadmium tin combined withabout 1% gallium.

WAYNE E. BLACKBURN.

REFERENCES CITED UNITED STATES PATENTS Name Date Wilson Mar. 12, mo

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